#btnToTop {
    display: none;
    position: fixed;
    bottom: 20px;
    left: 30px;
    z-index: 99;
    outline: none;
    color: white;
    cursor: pointer;
    padding: 15px;
    border: 1px solid rgba(0,0,0,.125);
    border-radius: 10px;
}

#btnToTop:hover {
    background-color: #555;
}